As materials for permanent magnet, Japanese patent publication Hei7-78269 (Japanese patent application Sho58-94876, the patent families include U.S. Pat. Nos. 4,770,723; 4,792,368; 4,840,684; 5,096,512; 5,183,516; 5,194,098; 5,466,308; 5,645,651) discloses (a) RFeB compounds containing R (at least one kind of rare earth element including Y), Fe and B as essential elements and having a tetragonal crystal structure with lattice constants of a.sub.o about 9 .ANG. and c.sub.o about 12 .ANG., and each compound is isolated by non magnetic phase, and (b) RFeBA compounds containing R, Fe, B and A (Ti, Ni, Bi, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sb, Ge, Sn, Zr, Hf, Cu, S, C, Ca, Mg, Si, O, or P) as essential elements and having a tetragonal crystal structure with lattice constants of a.sub.o about 9 .ANG. and c.sub.o about 12 .ANG., and each compound is isolated by non-magnetic phase. It is mentioned that the permanent magnet has a good property when (1) the above tetragonal compounds have an appropriate crystal grain size, (2) the compounds are the major phase, and (3) microstructure of the compounds mixed with the R-rich non-magnetic phase is formed.
According to Example 2 of the Japanese patent publication Hei7-78269, for example, an alloy of 8 atom % B, 15 atom % Nd and the balance Fe was pulverized to prepare an alloy powder having an average particle size of 3 .mu.m. The powder was compacted in a magnetic field of 10 kOe under a pressure of 2 t/cm.sup.2 and sintered at 1100.degree. C. for 1 hour in Ar of 2.times.10.sup.-1 Torr. The magnetic properties are: Br=12.1 kG, Hc=9.3 kOe, and (BH)max=34 MGOe. The major phase of the sintered compact is a tetragonal compound with lattice constants of a.sub.o =8.8 .ANG. and c.sub.o =12.23 .ANG.. The major phase contains simultaneously Fe, B and Nd, and amounts to 90.5 volume % of the sintered compact. As to the non-magnetic interface phase which isolates the major phase, a non-magnetic phase containing more than 80% of R occupies 4 volume % and the remainder is virtually oxides and pores.
Though said magnet shows excellent magnetic properties, the latent ability of the RFeB or RFeBA tetragonal compounds have not been exhibited fully. This may be due to the fact that the tetragonal compounds are not well-oriented to the c.sub.o direction since the R-rich phase isolating the major phase of the tetragonal compounds is an amorphous phase.